Wind turbines are used to produce electrical energy using a renewable resource and without combusting a fossil fuel. Generally, a wind turbine converts kinetic energy from the wind into electrical power. A horizontal-axis wind turbine includes a tower, a nacelle located at the apex of the tower, and a rotor having a central hub and a plurality of blades coupled to the hub and extending outwardly therefrom. The rotor is supported on a main shaft extending from the nacelle, which shaft is either directly or indirectly operatively coupled with a generator which is housed inside the nacelle. Consequently, as wind forces the blades to rotate, electrical energy is produced by the generator.
In a typical assembly process of a wind turbine, the tower is constructed and the nacelle is positioned on top of the tower at a significant height off of the ground level or sea level, as the case may be. The rotor hub may be coupled to the main shaft of the nacelle prior to placement of the nacelle atop the tower. Alternatively, the rotor hub may be coupled to the main shaft after the nacelle is placed atop the tower. In either case, at least one of the wind turbine blades, and in many cases all of the wind turbine blades, are usually coupled to the rotor hub in a separate assembly step after the rotor hub is positioned on the main shaft atop of the tower.
In such an assembly step, the root end of the wind turbine blade will generally be fitted with a plurality of connectors, which may take the form of stud bolts, about its circumference which extend longitudinally from the root end of the blade. The blade will then be lifted, typically with a crane system or the like, up to the top of the tower for attachment to the rotor hub. In this regard, the stud bolts at the root end of the blade will be generally aligned with corresponding through bores in the rotor hub and inserted therethrough. Once the stud bolts are positioned through the bores, a technician positioned in the interior of the rotor hub will secure fasteners to the ends of the stud bolts and thereby attach the wind turbine blade to the rotor hub.
Many modern wind turbines are pitch controlled and therefore provide for rotation of the wind turbine blade relative to the rotor hub about the blades longitudinal axis. The ability to pitch the blade is achieved through a pitch system having a pitch bearing at the interface between the blade and the rotor hub. In this regard, the pitch bearing includes an inner ring and an outer ring with a plurality of bearing elements (e.g., ball bearings) disposed between that allows the rings to rotate relative to each other. In many conventional wind turbine designs, the wind turbine blade is coupled to the inner ring of the pitch bearing and the outer ring of the pitch bearing is fixedly secured to the rotor hub. The pitch system further includes an actuator of one type of another that when actuated, rotates the blade about its longitudinal axis relative to the rotor hub.
When the pitch bearing is coupled to the rotor hub, the inner ring is typically accessible from an interior of the hub. The outer ring, however, is typically not accessible from the interior of the hub, but is instead accessible from an exterior of the hub. In such an arrangement, the pitch bearing, and more particularly the outer ring of the pitch bearing, may be coupled to the rotor hub while the hub is on the ground, deck of a ship, etc. and prior to the rotor hub being positioned atop the tower. For example, the pitch bearing may be coupled to the rotor hub at the manufacturing site such that the pitch bearing essentially forms part of the rotor hub. As can be appreciated, access to the hub and pitch bearing and coupling of the components are considerably simplified with the hub on the ground, deck of the ship, etc. It remains, however, that at least one of the wind turbine blades is coupled to the rotor hub when the hub is positioned atop of the tower at a significant height above ground level or sea level, as explained above.
In this regard, the connectors (e.g., stud bolts) extending from the root end of the wind turbine blade are inserted through bores in the inner ring of the pitch bearing. In current designs and as noted above, the inner ring of the pitch bearing is accessible from an interior of the rotor hub. Accordingly, a technician positioned within the interior of the rotor hub may secure fasteners to the connectors in order to attach the blade to the hub. To this end, the fasteners may be threaded nuts configured to cooperate with a threaded end of the stud bolts. The fasteners (e.g., nuts) may be fairly sizable and weigh anywhere between about 100 g and 500 g apiece, typically in the region of about 400 g apiece for a large wind turbine blade, such as a 60 m-80 m blade or larger. In a typical procedure, a container (e.g., box, bag, etc.) of nuts may be transported up through the wind turbine tower to the nacelle and located within or adjacent the hub. The technician may grab one or possibly a few nuts at a time and threadably engage the nuts with the stud bolts in a conventional manner. The technician may then easily access the container for additional nuts, since the technician and container are in close proximity to each other inside the hub, until all of the stud bolts have been fastened.
In recent years, there has been a significant increase in the overall size of wind turbines due to the desire to capture more of the wind's available energy. As the rotor hub, typically a casted component, has increased in size, the corresponding increase in material costs has presented a significant concern for wind turbine manufacturers. To address this concern, more recent wind turbine designs provide the inner ring of the pitch bearing coupled to the rotor hub and the wind turbine blade coupled to the outer ring of the pitch bearing (i.e., opposite to conventional designs discussed above). While such a design is effective for reducing material costs in manufacturing rotor hubs, this design change has presented other challenges for manufacturers. For example, with the wind turbine blade now coupled to the outer ring, the outer ring would not be accessible from the interior of the rotor hub. Hence, the technician must now be positioned at an external location where he/she can access the threaded ends of the stud bolts and apply a fastener thereto.
Modern rotor hubs typically consist of an inner hub frame that provides the structural aspects of the rotor hub and to which the pitch bearing and the rotor blades attach, and an outer cover, typically referred to as a spinner, which generally encloses the hub frame. The spinner generally protects the hub frame and related components, and provides a more aesthetic and aerodynamic configuration to the rotor at a central region of the rotor. Thus to access the outer ring of the pitch bearing, a technician will typically position himself/herself in the relatively confined space between the hub frame and the spinner. In this regard, the technician will grab one or a few of the relatively heavy fasteners, such as nuts (e.g., a pocket or pouch full) and then, via an access hole in the hub frame, position himself/herself outside the hub frame in the space between the hub frame and spinner in order to secure the nuts to the threaded stud bolts. When the technician depletes the limited supply of nuts on his/her person, the technician will exit the space between the hub frame and spinner, enter back into the interior of the hub (i.e., the interior of the hub frame), resupply himself/herself with another batch of nuts, and then climb back out into the space between the hub frame and spinner to continue securing nuts to the stud bolts. This process will then be repeated until all of the stud bolts, which may number as many as 180-200 bolts for current blade designs, have been secured with a nut.
Based on the above, it is clear that connecting the wind turbine blade to the outer ring of the pitch bearing has some drawbacks. Namely, securing fasteners to the connectors so as to couple the blade to the rotor hub is a difficult, labor intensive, and time-consuming process which increase costs. Additionally, it may not be uncommon for some of the fasteners to become unintentionally separated from the technician. For example, some fasteners may be dropped by the technician as he/she attempts to secure the fasteners to the connectors. Alternatively, fasteners may fall out of the technician's pocket or pouch and fall into the space between the hub frame and spinner. Such errant fasteners can cause damage and in any case must be removed before operation and are not easily retrieved from within that space.
Accordingly, there is a need for improved devices and procedures for coupling a wind turbine blade to a rotor hub that overcomes the drawbacks in current procedures for assembly of wind turbines.